Project Summary: Understanding how relations between physical activity and positive affect may alter affective neurocircuitry early in development holds enormous promise for unlocking the development, etiology, and treatment of mental illnesses, particularly mood disorders. Both childhood mood disorders and lack of physical activity are two major public health problems, the latter with increasing prevalence and associated with substantial morbidity across the lifespan1,2. Despite research implicating a strong role of physical activity in the amelioration of mood symptoms, research accounting for these developmental relationships relevant to the onset of mood disorders is greatly lacking. Novel, early interventions focusing on the benefits of physical activity for the prevention of childhood mood disorders may hold great promise. With this framework in mind, the purpose of this K23 proposal is to enable the candidate to develop a research program investigating the impact of physical activity on affective neural activity and risk for childhood mood disorders. To help achieve the goal, the training plan in this application addresses the applicant's need for training in: 1) physical activity and event related potentials (ERP) assessment methods [and protocols] in young children; 2) research assessments of emotion development and preschool psychopathology; and 3) longitudinal study design and advanced data analysis techniques. A rich training environment and a multidisciplinary team of mentors in each of these areas is detailed. The research proposal tests the hypothesis that positive affectivity (measured in terms of brain, behavior, and ecological momentary assessment) mediates the association between physical activity and later dimensional mood symptoms early in development. Thus, we hypothesize that low daily (and weekly) physical activity leads to lower daily (and weekly) positive affect and significantly contributes to the development of mood symptoms, even after accounting for key covariates such as family history of mood disorder and psychosocial risk and protective factors. To test these hypotheses, preschoolers (ages 3-5) high and low on positive affect will be recruited using a screening checklist and assessed twice, 18 months apart using ERP methods, one week of objectively collected physical activity data, one week of ecological momentary assessment data, and behavioral methods in a prospective design. Data from this study will be used to inform development for a more definitive R01 project that charts the trajectories of physical activity, neural markers, and mood symptoms in at-risk young children and results are anticipated to have prevention and treatment implications, by determining whether and how positive affectivity (measured behaviorally and neutrally) links physical activity to elevated mood symptoms early in development. Further, the proposed training plan will enable Dr. Whalen to become an independent scientist investigating the role of physical activity in the development and maintenance of mood disorders in children.